High-frequency electron discharge device



June 12, 1951 w. w. HANSEN HIGH-FREQUENCY ELEcTRoN DISCHARGE DEVICE Filed Dec.

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assigner to The Sperry Corporation, a corporation of Delaware Application December 28, 1946, Serial No. 719,099

9 Claims.

This invention relates in general to the production of ultra-high-frequency energy through the use of magnetron-type tubes, and in particular, is concerned with improvements in the operation of magnetrons using resonant cavity chambers.

In the usual cavity-resonator magnetrons whose ultra-high-frequency output is produced in pulses, the oscillations of one pulse bear no definite relationship With the oscillations of successive power pulses, That is, during any power pulse, the phase of the oscillations is indeterminately different from that of the oscillations of a different pulse. The control of the phase of the oscillations is highly desirable in many micro- Wave sources. Such sources are usually called coherent oscillation sources, as distinguishable from otherwise incoherent pulsed oscillators.

Another difficulty experienced in the use of magnetron oscillators which are pulsed is in the length of time it takes for the oscillations of any pulse to reach full amplitude. In fact, if the'pulse is of sufficiently short duration and the build-up time is of suicient length, it is possible that the oscillations of a single pulse never reach their full strength or intensity, and the device fails to oscillate as desired. f

A still further diiiiculty experienced Withv the use of a magnetron as a pulsed oscillator is termed mode-hopping. This is the expression used to describe the diiiiculty that occurs when the cavity resonators, which are the frequency determining elements in the magnetron, suddenly change their mode of oscillation. The frequency of oscillation is, tc a .great degree, determined by the physical dimensions of the cavity resonators making up the magnetron. However, a small shift in frequency is noted as the mode of oscillation is changed. YIn most applications this is highly undesirable, and preventative meas# ures are usually taken to `prevent the occurrence of such mode-hopping between pulses.

It is, therefore, an object of the present invention to provide an improved magnetron oscillator having a pulsed output, the phase of the oscillations in each successive pulse being controlled.'

It is a further object of the present invention to provide excitation means for a pulsed cavity resonator magnetron oscillator for causing the oscillations of each pulse to build up more readily and reliably in the resonators.

t is another object ofthe present invention to provide excitation means for a cavity resonator magnetron oscillator Whose output energy consists of recurrent pulses, such means prohibiting the resonator from changing its modeof os- (Cl. Z50-27 .5)

cillation between pulses and thereby maintaining the output frequency constant.

It is a still further object of the present invention to provide a convenient means for the'introduction of energy vinto the magnetron from the excitation means described in the above objects.

The invention in another of its aspects relates to novel features of the instrumentalities described herein for achieving the principal objects of the invention and to novel principles employed in those instruinentalities, Whether or not these features and principles are used for the said principal objects or in the said field'. 'Y

A further object of the invention is to provide improved apparatus and instrumentalities embodying novel features and principles, adapted for use in realizing the above objects and also adapted for use in other fields.

In order to achieve the above objects, theresonators of the magnetron are, in accordance with the present invention, made to oscillate continuously at a 10W level by the introduction of Aa small amount of high-frequency energy from an auxiliary oscillator, thus providing a predetermined minimum energy level for the resonator oscillations. The high-'frequency energy, which assures the maintenance of a 10W-level iield, may easily be fed into a magnetron of the cold-cath'- ode type by the teachings of the present invention. Asis Well known, such a cathode operates upon the principle of secondary emission, and requirespa primary source of electrons. This primary source of electrons is supplied byv a so-called starting filament. In general, such a filament is heated suiciently to cause it to emit electrons. The lament is usually positioned close to the cathode, or secondary emitting surface, so that some of the emitted electrons strike the cathode, causing the secondary emission. Theree after the starting lament may, in some cases, be de-energized.

The high-frequency control energy, which it is desired to feed into the magnetron, may be introduced by means 'of this starting filament, which is used as one of the input electrodesand the shell in which is formed the cavityre'son'ators as the other, whereby the low-level field is thus created Within the space surrounding the filament and cathode, and in the cavity resonators themselves. The presence of the loWQlevel eld is sufcient to velocity modulate the electron cloud so that, when the magnetron is pulsed, that is, when a high potential is applied momentarily between the cathode and the cavity resonator Shell theresulting oscillations Will occur most easily at the frequency of the low-level eld. As this frequency is adjusted or selected to be the same as the resonant frequency of the cavity resonators operating in a particular desired mode, it is readily seen that there is a strong inclination for the magnetron resonators to oscillate in this mode and little likelihood of oscillations occurring in an undesired mode. Since the lowlevel eld exists prior to the pulse, there is no danger of the magnetron changing its mode of oscillation between pulses.

Furthermore, not only is the frequency of the high-level high-frequency energy controlled or suggested by the low-level field, but the phase of the resulting high-level oscillations is also controlled. This is true since the magnetron, when pulsed, merely causes, in affect, the amplitude of the already existing low-level field to be greatly increased. Actually, the magnetron itself acts as an oscillator, separate and apart from the auxiliary oscillator, but because of the frequency and phase lock-in effect, it may from one viewpoint, be considered as an ultra-high-frequency amplifier.

Since the energy fed into the magnetron creates a ield having a predetermined minimum energy level, it is easily seen that the oscillations, which occur when the magnetron is pulsed reach full amplitude in a much shorter time than if the low-level eld were nonexistent. Because of this decrease in build-up time, it is possible to have high-level ultra-high-frequency oscillations produced and sustained in the resonator with pulses of very short duration.

The achievement of these and other objects by the present invention will become more apparent from the following description, taken in connection with the accompanying drawing wherein:

Fig. 1 is a top view of the magnetron tube with parts removed and cut away; and

Fig. 2 is a section view of Fig. 1 taken along line 2 2 thereof.

Referring now more particularly to Fig. 1 which is a top view of a cavity resonator type magnetron having a cylindrical-shaped cathode II placed in the center of a thick-walled, cylindrical-shaped resonator block or anode member I2 which has an even number of radially disposed cylindrical cavity resonators I3 formed in the conducting walls of the resonator block I2, the axes of the resonators I3 being parallel to the axis of the resonator block I2. Each cylindrical resonator cavity I3 is connected to a common cylindrical interspace I4 between the inner wall I5 of the anode block I2 and the surface of cathode I I, by a narrow radial slot IE which extends the length of resonator I3.

Cylindrical cathode I I is of the secondary emission type having its surface coated with a material which emits an abundance of electrons when it is bombarded with a small number of electrons from a primary source. A lament 20, supported longitudinally along the axis of a semicylindrical depression 2l in cathode II, supplies the primary electrons when it is heated to emit ting temperature. The axis of the cylindrical depression 2I, along which filament 2i) lies, is parallel to the axis of cathode i I and is spaced from it by a distance substantially equal to the radius of cylindrical cathode II.

Fig. 2, which is a sectional view of Fig. 1 taken along line 2-2, shows how cathode I! and filament 20 are supported. Auxiliary equipment is diagrammatically shown in this view to further aid in explaining the present invention.. AS. Qian..

be seen, anode member I2 has its ends closed by a pair of end plates 3B and SI which nest into rims or flanges 32 and 33 formed at each end of the cylindrical resonator block or anode member I2. The seal between the end plates 3i) and 3l and the anode member I 2 at the rims 32 and 33 is made airtight to permit later evacuation of the magnetron tube. Cathode II is mechanically supported along the axis of anode member i2 by the end plates 30 and 3l. A disc of insulating material 34 separates the lower end 35 of cathode I I from the bottom plate 30. A similar insulating disc 36 separates the upper plate 3i from the upper end 31 of cathode l I. A cathode lead-in 39 passes through an insulating bushing 38 and insulating disc 36 to cathode EI without shortcircuiting to upper end plate 3|. Since the cathode II is insulatedly supported within the resonator anode member l2, a potential difference may be applied between these two elements, lead-in 39 serving as the conducting terminal for cathode I I, and inner Wall I5 of anode member I2 serving as the anode face surface.

The upper end of lament 2) is connected to lead-in member 25 which is mechanically supported by a glass airtight s eal 4i! within a short section of lconducting tubing 4I which is inserted into the upper end plate 3 I. The externally protruding end of tubing section 4l and the extended end of lead-in member 25 form a short section of coaxial line. External threads 42 may be provided on the outer wall of section 4I near its extreme end to permit mechanical coupling to a lead wire which is diagrammatically shown as 43.V

'I'he lower end of lament 2li is connected to lead-in member 2B which is mechanically supported in a similar fashion by a glass airtight seal 45 within a section of conducting tubing 46 inserted into the lower end plate 3B. As before, tubing section 46 and extended lead-in member 26 form a short section of coaxial line.

Tubing section 45 is deliberately made longer than section 4I and has a second glass seal 41 at its extreme end to provide greater mechanical rigidity for lead-in member 25. External threads 48 may be provided on the outer wall of tubing section 46 near its end to permit mechanically coupling to a coaxial line which is shown dia-Y grammatically as 49.

A coaxial T-section 5i? is provided in the sec'' tion of coaxial line formed by tubing section 4S and lead-in member 25. This T-section lill is provided with threads 5I near its end to permit the connecting of second lead wire 52 to filament 20 through lead-in 26.

Coaxial line 49 connects an ultraor superhigh-frequency oscillator @il to the coaxial line section formed by tubing section 45 and lead-in member 26. Condensers 21 and 28 are inserted in both legs of coaxial line 49 to permit thealternating frequency output of oscillator to pass unhindered while preventing any direct current from passing along the line 49. Lead wire 52 connects one terminal of a battery @I to one end of filament 2D and connecting lead Wire 43 connects the other terminal of battery 6I to the opposite end of nlament 20.

A high Voltage power supply 62 has its positive terminal connected by a lead wire @-3 to the resonator block I2. For reasons of operating safety, this lead Wire 63 is usually cart-hed so that the resonator block l2 operates at ground poten` tial. The negative terminal of the high voltage power supply E2 is connected by a lead wire 64 to the cathode lead-in terminal 33, Since terminal 3,9 is insulated from the resonator block I2 by insulating bushing 38, the output voltage of the power supply t2 is applied between the conductving resonator block I2 and the cathode II.

The oscillations generated kin the magnetron may be led from the tube by means of a-coupling loop il!) located in one of the resonators I3, One end of the loop Sii is fastened to the wall of resonator'IS and the other end passes through an aperture 85 in resonator shell I2 and isconnected to a lead wire SI which passes through a glass seal 82 to form the center conductor of a coaxial 'output connection, with'the outer conductor being forme-d of a tubular member 83 sealed to the outer wall of anode member I2. Threads ttl-may be provided on the outer wall of tubular member 84 for easy and eiiicient connection to a coaxial coupling line, not shown, through which the high frequency oscillations generated by the magnetron may be conducted to a suitable utilization circuit.

In the operation of such a cavity resonator magnetron, a magnetic eld is supplied which is directed along the axis of the tube. For simplicity, the source of such a magnetic iie'ld is omitted from the accompanying drawings. lt may be an electromagnet with the tube pla-ccd between the pole pieces, or a simple permanent magnet may be used to supply the magnetic iield along th tubes axis.

Filament 2t is heated to an emission tempera* ture by passing an electric current therethrough, the necessary potential being supplied by battery SI connected to filament by means of leads :52 and IIS. Some of the electrons emitted by `filament 2li are attracted to the cathode I I by a battery 'i0 connected therebetween. Since the surface of cathode I I is coated with a material which emits an abundance of electrons upon bombardment, a large number of secondary emitted electrons are produced.

If a potential is applied between cathode IfI and the anode member I2 by the high voltage power supply 62 with the anode member IZ being connected to the positive lead t3, the resulting electric iield will cause the secondaryV electrons emitted from cathode iI to travel substantially in a radial direction away from cathode I I. However, these outwardly moving electrons will also be affected by the axially directed magnetic iield which causes them to move at right angles to the radial direction. The resulting of the electrons will thus be iniluenced by the combined effect of the electric and magnetic eld. As a result, the electrons will be whirled in the interspace It past the slots I5 which connect inner space i@ with the cylindrical resonant chambers I3. By the proper adjustment of the electric and magnetic fields of the magnetron, it is possible to maintain this whirling cloud of electrons in the interspace Iii with cathode I I supplying new electrons to the cloud to replace those which strike the anode face surface I5.

The 'whirling cloud of electrons gives up some of its energy as it passes by slots i5 and initiates or reeniorces electromagnetic oscillations within the cylindrical resonators It. This is possible since the standing waves established within the resonators I3 by the electromagnetic oscillations created therein causes the instantaneous polarity of adjacent anode face surfaces I 5 to be opposite. If the whirling cloud or electrons passes by slot It at the instant that the polarity of a pair or" adjacent anode face surfaces tends to oppose .its motion, some o f the energy of the whirling cloud v pulses.

is given up to'this opposing lield. This energy reenforces the electromagnetic oscillations within the resonator I3 and oscillations are thereby maintained in the system.

If the potential that is supplied vby high voltage power supply til is maintained constant, the oscillations which are set up in cylindrical resonators I3 will be sustained and electromagnetic energy may be removed from the resonator I3 by means of a conventional coupling loop 8S located in one of the resonators I3. The output of the magnetron in such a case will be of the continuous wave type; that is, it will bea continuous train of oscillations whose amplitude will remain constant and whose frequency will be determined by the physical dimensions of cylindrical resonators I3 and the mode in which they are oscillating. However, in many applications itis desirable to produce pulses of oscillations rather than a continuous train. rlj'his is accomplished by pulsing the high voltage power supply 62. If this is done, oscillations will be set up in the resonators I3 only during those intervals when power supply 62 supplies potential between cathode II and resonator shell IZ. Several problems arise in such a case, as has been discussed above, First, the oscillations ci any one pulse bea-r no definite relationship with the oscillations of successive power pulses. Since in many microwave systems it is desirable to control the phase oi' oscillations in successive power pulses, some method oi synchronizing or adjusting the phase of oscillations in each succeeding pulse is required. Further'- more, if the magnetron oscillator is pulsed, it takes a finite time for the oscillations generated in the resonators it to reach full amplitude. If the pulses are of extremely short duration and the build-up time of oscillations is relatively lengthy, it is possible to reach a condition where the oscillations oi any single pulse never reach their full amplitude and the device fails to operate as desired.

Another *diiiiculty when Vpower supply is pulsedis that the cavity resonators I3 will occasionally change their mode oi oscillation between Since the irequency'output is a function of the mode of oscillation as well as vthe physical dimensions ofthe resonators I3, this causes the cutput'irequency of the magnetron tube to shift, which is highly undesirable.

To overcome rthese difficulties, low-power oscillator Sii is connected to filament 2o anode member I2 through coaxial line t9. The outer conductor of coaxial line is electrically connected to anode member I2 through tubing iii and end plate 3S. The center conductor ci coaxial line 4i) is connected to lilament iii through lead-in member 25. The ultra high frequency energy-output of oscillator `thereby sets up an electric field in interspace Ifl between filament 2@ and anode face surfaces iii. 'lhe frequency oivoscillator 6I! Yis-adjusted to be that oi the resonant frequency of resonators i3 when they are oscillating in ktheir preferred or desired mode. The .presence or" this high yfrequency lcwinten-n sity eld Ain interspace iii aids in overcoming `the difliculties encountered in pulsing the magnetron. y

When power supply is pulsed, the electrons which travel toward resonator shell Iii. under the influence .of the field between cathode il and `anode member vI2 are already influenced byv the Ypre-'enisting low-level ileld supplied by low-power oscillatorii andthus have a preferred frequency Vci oscillation with a definite phase relatiOnShip to the oscillations of the preceding pulse. As a result, the oscillations which are generated in resonators I3 are merely amplified versions of the field oscillations in interspace ld. The frequency and phase of these oscillations are identical with the frequency and phase of the output of oscillator Si). Because of this controlling or lock-in effect exhibited by the low-level field existing in interspace lli, there is little danger of mode-hopping occurring between successive pulses of power supply 52. Furthermore, the phase of oscillations in the recurring pulses are completely controlled by the output of oscillator 60. Also, it is easily seen that the build-up time is reduced by this system, since a pre-existing minimum level of alternating field is already existing in the magnetron interspace region i4 prior to the pulsing of power supply e2. For that reason, the oscillations of the output pulses need not be built up from zero but merely from this pre-existing low-level iield.

The present invention provides a most convenient method for introducing this controlling energy into the magnetron and for setting up the low-level field in the interspace region ill. The presence of the filament 2&3 is required in the operation of the secondary emission type cathode and in general is electrically insulated from it. Battery 5l may sometimes be disconnected after the tube has begun operation, since some electrons fall back on cathode H and generate further secondary electrons to continue operation.

Thus, without the introduction of new elements or members, but merely by utilizing an already present and necessary element in the tube, it is possible to greatly increase the frequency stability of the magnetron. Furthermore, if the tube is to be pulsed, it is possible to control the phase of the oscillations in the pulses, minimize build-up time and eliminate the danger of mode-hopping.

The filament in this description is shown to be of a rod-type supported in a semi-cylindrical depression in the cylindrical cathode surface. The coaxial line method of feeding the controlling energy as described is thought to be eXtremely convenient and easy to manipulate. The lead from the low-powered local oscillator may be connected to and disconnected from the magnetron without interfering with any of the other connections to the magnetron and Without disturbing the system. However, it is not intended to limit the scope of the present invention to the described filament-cathode disposition, but it is intended to embrace other constructions which utilize a filament as the source of primary electrons and a cathode as a source of secondary omitted electrons, the filament and cathode having no direct electrical connection with each other.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electron discharge device comprising a cylindrical cathode having a semi-cylindrical depression in its surface, said cathode being of the secondary emitting type, a filament member supported along the axis of said semi-cylindrical depression, means defining a plurality of cylindrically arranged anode faces surrounding said cathode and mutually separated by a plurality of longitudinal slots, means dening a like plurality of cylindrical cavity resonators each having a longitudinal slot in its wall, said last slots com'- municating with said iirst-named slots, a source of electromagnetic oscillations, and means connecting said source between said filament and said anode.

2. An electron discharge device comprising a cylindrical cathode of the secondary emitting type, a substantially cylindrical anode member surrounding said cathode, said anode member having a plurality of apertures and defining also a like plurality of cavity resonators communicating with said apertures, a filament positioned intermediate said cathode and said anode member,

A a source of electromagnetic oscillations, and

means connecting said source between said lament and said anode member.

3. An electron discharge device comprising a cathode, means dening a plurality of anode faces surrounding said cathode and separated by a like plurality of slots, means defining a like plurality of cavity resonators each having an aperture in the resonator wall, said resinator wall apertures communicating with said slots, a lament positioned intermediate of said cathode and said anode faces, a source of electromagnetic oscillations, and means connecting the output terminals of said source between said filament and said anode faces.

4. An electron discharge device comprising a cylindrical cathode of the secondary emitting type, a substantially cylindrical anode member surrounding said cathode, said anode member having a plurality of apertures and defining also a like plurality of cavity resonators communicating with said apertures, a filament positioned intermediate said cathode and said anode member, means connected to said anode member and said iilament producing an alternating electromagnetic field between said anode member and said filament, means adjacent said anode member producing a magnetic eld parallel to axis of said cylindrical cathode, and means connected to said cathode and said anode member for producing a pulsating electric eld between said cathode and said anode member, whereby high frequency electromagnetic oscillations are generated in said cavity resonators in phase with said alternating electromagnetic field.

5. An electron discharge device comprising a cylindrical cathode, means deiining a plurality of cylindrically arranged anode faces surrounding said cathode and mutually separated by a plurality of longitudinal slots, means dening a plurality of cylindrical cavity resonators each having a longitudinal aperture in its wall, said last apertures connecting with said first-named slots, an electro-de positioned intermediate said cathode and said anode faces, means connected between said electrode and said anode face for producing an alternating electromagnetic field between said electrode and said anode face, means adjacent said anode face means for producing a magnetic iield substantially parallel to axis of said cylindrical cathode, means connected between said cathode and said anode faces for producing an electric field between said cathode and said ano-de faces, and means connected to said electric iield producing means for pulsing said electric field, whereby said alternating field between said anode faces and said electrode 9 controls the phase and frequency of electromagnetic oscillations generated in said cavity resonators. Y

6. An electron discharge device comprising a source cf electrons, means dening a plurality of anode faces surrounding said source and separated by a like plurality of slots, means defining a like plurality of cavity resonators each having an aperture in its resonator Wall, said resonator wall apertures communicating with said slots, an electrode positioned intermediate said source and said anode faces, and means connected to said electrode and said anode face means for producing an alternating electromagnetic eld extending between said anode face and said electrode.

'7. An electron discharge device comprising a cathode, an anode member surrounding said cathode and defining a plurality of resonant circuits, an electrode positioned intermediate said cathode and said anode member, and means connected to said electrode and said anode member supplying an alternating electromagnetic field extending in the interspace between said anode and said electrode.

8. A system for an electro-n discharge device, comprising a cathode, an anode member surrounding said cathode and defining an interspace therebetween, an electrode positioned in said interspace, a plurality of cavity resonators defined Within said anode member, each of said cavity resonators communicating with said interspace through an aperture in said resonator wall, and means external said anode member for supplying an alternating electromagnetic field eX- tending between said anode member and said f electrode in said interspace.

' each lead-in member providing hermetical seals.

WILLIAM W. HANSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,114,114 Roberts Apr. 12, 1938 2,163,157 Samuel June 20, 1939 2,409,038 Hansell Oct. 8, 1946 2,438,194 Steele, Jr., et a1. Mar. 23, 1948 2,450,763

McNall Oct. 5, 1948 

